Hundreds of people looked on as the beacon at Nelson's flagship HMS Victory in Portsmouth was lit, sending a flame high into the night sky. Other members of the Royal Family lit beacons around the UK, starting with the Prince of Wales on Church Green, Ballater, near Balmoral.
Earlier in the day, crews of British, French and Spanish warships laid wreaths off Cape Trafalgar where Lord Nelson's victory saved Britain from invasion by Napoleon's forces.
The events started with the laying of wreaths in the crypt of St Paul's Cathedral and, as the "Last Post" was played at the spot on HMS Victory where Nelson fell,the admiral's signal to his fleet: "England expects that every man will do his duty", was hoisted.
At a dinner in Nelson's Great Cabin on the ship, the First Sea Lord, Admiral Sir Alan West, said: "This very night 200 years ago, still unknown to the nation, a great sea battle had been won. The architect of that victory was tragically struck down and lay dead below in this, his flagship - killed at the moment of his greatest triumph."
Sir Alan added that he was amazed how the anniversary had "gripped the spirit of Britain". The wreath-laying ceremony off Trafalgar, west of the strait of Gibraltar, where 7,000 sailors lost their lives, was conducted by French frigates, HMS Chatham and Montcalm and the Spanish carrier Principe De Asturias.
Speaking in Cadiz, Count Andre de Villeneuve, a fifth-generation descendant of the French admiral who led the Franco-Spanish fleet on the day, said: "It was very moving. At the same time it was a gesture of reconciliation between former combatants 200 years after the event. It shows we don't forget the horror and sacrifice of that battle."
The celebrations had been planned for two years. They will end tomorrow with a parade in Trafalgar Square.
Nelson was killed by a French sniper's bullet and his funeral, the first state ceremony for anyone outside the royal family, lasted for five days.Reuse content